The present invention relates to sports racquets, for example tennis, squash, badminton, and racquetball racquets. Such racquets have a head portion containing an interwoven string bed, a handle, and a shaft portion connecting the head portion to the handle.
Most high performance sports racquets have a frame molded from composite materials, e.g., a carbon fiber-reinforced resin. Holes for anchoring the ends of the strings are drilled through the frame after the racquet is molded. Plastic grommet pegs, which are formed on a grommet strip or bumper strip that rests against the outside surface of the frame, extend through the string holes to protect the strings from the sharp edges of the drilled holes.
Proposals have been made to form string holes during the molding process. For example, commonly owned U.S. Pat. No. 6,800,239 discloses a racquet made of two frame tubes, in which the string holes are formed during the molding process using a plurality of hole-forming pins positioned within the mold between the two tubes. Such racquet has the advantage that it does not require drilling holes through the material, which can weaken the frame. Moreover, the two tubes press against one another during molding, forming an interior support wall, which further strengthens and stiffens the racquet.
Commonly owned PCT application WO 2004/075996 discloses another sports racquet in which the string holes are molded-in. In this racquet, however, pairs of adjacent conventional string holes are replaced with a single enlarged string hole, the opposite sides of which accommodate two strings. Such process allows the weight of the racquet head to be reduced and, as in the case of the '239 patent, tends to produce a frame which is stiffer and stronger than one in which string holes are drilled through the frame after molding.
In racquet sports, there is no single ideal racquet. Different players need racquets with different playing characteristics. For example, beginners, intermediate players, and advanced players each tend to prefer racquets with different playing characteristics. Also, a player's choice of racquet tends to vary depending upon the player's type of swing and playing style. Serve-and-volley players may prefer racquets with far different playing characteristics than racquets preferred by baseline players.
Once a racquet has been designed and built, it is difficult to alter its playing characteristics to any significant degree. Its overall weight, stiffness, balance, mass and polar moments of inertia, sweet spot, and coefficient of restitution are determined principally by the design of the frame, choice of material, the fiber orientation of the various plies of material forming the frame, and the number and placement of the string holes. The weight, balance, and moments of inertia can be modified to some degree by using special tapes positioned at certain racquet locations, or by attaching removable parts. However, such measures make the racquet heavier than its original design, which is normally undesirable. Moreover, the frame stiffness and the stringing pattern of the racquet cannot be changed after the racquet has been molded and the string holes formed. In order to substantially modify the playing characteristics of an existing racquet model, the racquet frame would have to be redesigned.
In order to satisfy a range of player needs, manufacturers currently are forced to offer many different racquet models. It would be desirable to provide a racquet whose playing characteristics can be customized after the racquet is manufactured in order to reduce the number of racquet models while still providing a wide range of playing characteristics.